1. Field of the Invention
The invention relates to the field of fluid distribution, including both liquids and gasses, and in particular to a multiple input and multiple output valving system employing self-cleaning valves having minimal dead volume.
2. Description of the Background Art
Valving systems for controlling or regulating fluid flow are widely known and are used in a variety of applications. For example, valving systems are commonly used in the chemical and biochemical industries where different fluids are often mixed to obtain a desired end product. In such applications, the fluids are commonly delivered to a mixing chamber through a plurality of fluid lines. To control flow of the fluid through the lines, a variety of valves can be employed. The valves are opened and closed at appropriate times to deliver the fluids for mixing. After mixing, the valves can again be operated to distribute the mixed fluid for further processing, storage, delivery, or the like.
In one particular application, such a valving system is included in a chemical synthesizer which synthesizes diverse collections of molecules on a plurality of solid supports such as beads. An exemplary chemical synthesizer employing such a valving system is described in U.S. patent application Ser. No. 08/149,675, filed Nov. 2, 1993, the disclosure of which is herein incorporated by reference. Such a synthesizer employs a parent vessel to mix bead suspensions. The mixed beads are distributed through a common manifold to a plurality of reaction vessels. In the reaction vessels, the beads are exposed to different, selected monomers, which react on the beads to be coupled thereto. Examples of the use of beads with diverse molecular products synthesized thereon are disclosed in U.S. patent application Ser. No. 08/146,886, filed Nov. 2, 1993, the disclosure of which is herein incorporated by reference. The beads are then recombined through the manifold back to the parent vessel and mixed. The mixed bead suspension is then again divided among the plurality of reaction vessels, and the process of monomer addition, bead mixing, and redistribution continues. In such a process, a variety of valves are employed to distribute the fluids between the parent vessel and the reaction vessels and to introduce the reagents to the reaction vessels. Although the valves described in U.S. patent application Ser. No. 08/149,675 have proven to be effective, various improvements are desired.
For example, a common valve employed in such chemical synthesizers is a two-way plunger valve, commercially available from Applied Biosystems or General Valve Corp. The plunger valve has an input port and output port that are in communication with a central chamber. To close the valve, a plunger is pushed against a membrane which removes any fluid from the chamber and forms a seal between the input and output ports. In so doing, particulates, such as reagent beads or precipitation, which often collect in the membrane become smashed or trapped by the plunger. After continued use, the valve membrane becomes damaged by smashed particulate and fluid leaks even when the valve is closed.
One particular drawback of many valving systems, including the valving system of the above-referenced chemical synthesizer, is the limited number of input and output ports. Even three-way valves can sometimes be too limiting. Furthermore, as more ports are included, the size of the valves can become unduly large. For example, in some systems the three-way valves are connected in series to form a manifold. However, the combination of the three-way valves in this way can be problematic because of the size of the resulting manifold. This in turn unduly increases the overall size of the apparatus and requires more fluid.
Another drawback of many valving systems is that the valves are normally in an open state and require actuation by a power source to close the valves. Such a configuration can be undesirable if a power failure occurs while the valves are closed. In such a case, the valves return to their open state allowing reagents to drain from the fluid lines.
In yet another drawback to many valves, the cross-sectional area of the chamber connecting the input and output ports is often greater than that of the fluid paths. This can be problematic if mixing is desired to take place in the chamber. Because of the different sized cross-sections, complete mixing within the valve is difficult to obtain.
In still another drawback, many valving systems employ extensive tubing to connect the valves. Use of such tubing, however, requires more fluids to be introduced into the system to insure sufficient fluid is present for distribution through the system. This in turn can increase operation costs and reduce efficiency.
Another consideration in the design of valving systems in many chemical applications is the need for the valves to handle aggressive reagents or other fluid media. This can often limit the type of materials used to construct the valves.
For these and other reasons, it would be desirable to provide a valving system which could overcome or reduce such problems. Such a system should be tolerant to aggressive media and particles and should be self-cleaning. The system should also allow for multiple inputs and multiple outputs while maintaining a relatively small size and employing minimal tubing. Further, the valving system should provide for improved mixing within the valve chambers.